1. Field of the Invention
The present invention relates in general to a method of disinfecting a contact lens and a disinfecting liquid used for the method, and more particularly to a technique for disinfecting the contact lens using the disinfecting liquid which is capable of exhibiting an excellent disinfecting effect.
2. Discussion of the Related Art
Conventionally, contact lenses are classified into non-water-contained contact lenses and water-contained contact lenses, or hard contact lenses and soft contact lenses. During a long period of use of the contact lenses, microorganisms such as bacteria and fungi tend to adhere to and proliferate on the surfaces of the contact lenses while the contact lenses are stored after they have been removed from the eyes. Such microorganisms may cause infectious diseases, giving adverse influences on the eyes of the user. In view of the above, the contact lenses need to be disinfected before they are worn on the eyes. In particular, it is indispensable to disinfect the soft contact lenses since the microorganisms are likely to proliferate on the surfaces of the soft contact lenses more often than on the hard contact lenses, increasing a risk of causing the infectious diseases.
For disinfecting the contact lenses, there have been principally practiced a thermal disinfecting method using a suitable boiling and disinfecting device, and a chemical disinfecting method using a suitable chemical agent such as a germicide or a preservative. The thermal disinfecting method undesirably requires a time-consuming boiling operation to disinfect the contact lenses. Accordingly, in recent years, the chemical disinfecting method has been widely employed to disinfect the contact lenses.
In the chemical disinfecting method, the contact lenses are immersed in a disinfecting liquid agent which contains a suitable germicide or preservative, so that the contact lenses are disinfected. As the germicide or preservative contained in the liquid agent, chlorhexidine, benzalconium chloride and thimerosal are disclosed in JP-A-52-109953, JP-A-62-153217 and JP-A-63-59960.
In order to obtain a sufficiently high disinfecting effect, the germicide or preservative as the chemical agent such as chlorhexidine is contained generally in a relatively high concentration in the disinfecting liquid agent. In this case, the germicide or preservative is likely to be adsorbed on the contact lenses on a molecular level, deteriorating wettability at the surfaces of the contact lenses, and causing a change in the properties and configuration of the contact lenses. In some cases, the adsorption of the germicide or preservative on the contact lenses may cause various troubles with the eyes while the contact lenses are worn on the eyes.
To keep the properties and configuration of the contact lenses unchanged, and assure a high degree of safety with the eyes of the lens users, the contact lenses may be disinfected by using a disinfecting liquid agent in which the germicide or preservative is contained in a relatively low concentration. In this case, however, the disinfecting effect to be exhibited by the liquid agent is inevitably lowered, causing contamination of the contact lenses by the microorganisms. Accordingly, when the contact lenses are disinfected by using such a conventional liquid agent, it is necessary to exercise an utmost care in adjusting the concentration of the germicide or preservative included in the liquid agent, making the disinfecting treatment of the contact lenses cumbersome.
The germicide or preservative contained in the contact lens liquid agent used in the chemical disinfecting method acts directly on the microorganisms such as bacteria, thereby exhibiting its disinfecting effect. Accordingly, the germicide or preservative is gradually decomposed and dissipated during use of the liquid agent, so that the liquid agent does not exhibit its disinfecting effect to a satisfactory extent. Thus, it is inevitably impossible to repeatedly use such a contact lens liquid agent, increasing an economical burden on the lens users.
The present invention was developed in the light of the background art described above. It is a first object of the present invention to provide a novel method of disinfecting a contact lens using a disinfecting liquid which exhibits an excellent disinfecting effect over a long period of time and which is easy and safe to handle.
It is a second object of the invention to provide a contact lens disinfecting liquid which is advantageously used to practice such a disinfecting method.
As one example of a photocatalyst which absorbs a light and exhibits a high degree of oxidation power on its surface, a titanium oxide is generally known. The titanium oxide has been recently attracting an attention since the titanium oxide exhibits a germicidal action with respect to pathogenic microorganisms based on its oxidation power. It is never known to use the titanium oxide having the germicidal action for disinfecting the contact lenses. Up to now, no techniques have been known to effectively disinfect the contact lenses using the titanium oxide.
An extensive study made by the inventors of the present invention under these situations has revealed that the contact lenses can be effectively disinfected by immersing the contact lenses in a suspension which is obtained by dispersing a titanium oxide in the form of fine particles in an aqueous medium, and irradiating the suspension with a light. The present invention was developed based on the above findings.
The above-indicated first object of the present invention may be attained according to a first aspect of the present invention, which provides a method of disinfecting a contact lens comprising the steps of preparing a disinfecting liquid which contains water-dispersible fine particles of a titanium oxide dispersed in an aqueous medium; immersing the contact lens in the disinfecting liquid; and irradiating the disinfecting liquid in which the contact lens is immersed, with a light.
The present method of disinfecting the contact lens utilizes the germicidal action of the titanium oxide based on its photocatalytic action. In the present invention, the water-dispersible fine particles of the titanium oxide are used to provide a disinfecting liquid. Namely, the disinfecting liquid is constituted by a suspension obtained by dispersing the water-dispersible fine particles of the titanium oxide in a suitable aqueous medium, and the contact lens is immersed in the thus prepared disinfecting liquid. With the contact lens being immersed in the disinfecting liquid, the disinfecting liquid is irradiated with a light for disinfecting the contact lens.
In the present method, the fine particles of the titanium oxide are uniformly dispersed in the disinfecting liquid in which the contact lens is immersed, without being aggregated or conglomerated, and these fine particles of the titanium oxide are uniformly irradiated with a light, so that the fine particles of the titanium oxide provide the germicidal or disinfecting action based on the oxidation power exhibited upon exposure to the light. The germicidal or disinfecting action of the fine particles of the titanium oxide which are uniformly dispersed effectively works on the entire surfaces of the contact lens, whereby the contact lens can be sufficiently disinfected. The fine particles of the titanium oxide serving as an effective disinfecting component do not act directly on the microorganisms such as bacteria, but functions as a catalyst. Accordingly, the fine particles of the titanium oxide are not decomposed or dissipated during use of the disinfecting liquid, and exhibit a long-term or permanent disinfecting effect, permitting a repeated use of the disinfecting liquid. Thus, the present arrangement allows an easy and economical disinfecting treatment of the contact lens.
The fine particles of the titanium oxide included in the disinfecting liquid as the effective disinfecting component is not a chemical agent which causes a chemical reaction, and is not likely to be adsorbed on the contact lens upon using the disinfecting liquid, therefore, it is not necessary to take into account adverse influences such as a change of the lens properties or configuration, and various troubles of the eyes of the lens users, which adverse influences are experienced when a contact lens liquid agent including a conventional germicide or preservative is used to disinfect the contact lens. Accordingly, the present arrangement assures safe and easy handling of the disinfecting liquid, and a simple disinfecting treatment of the contact lens.
In a preferred form of the above first aspect of the present invention, the fine particles of the titanium oxide have an average particle size of not larger than 15 nm. Preferably, the fine particles of the titanium oxide are contained in the disinfecting liquid in a concentration of 1100 ppm. These arrangements permit the disinfecting liquid to have a sufficiently high degree of transparency, so that the light is effectively incident on the fine particles of the titanium oxide, for thereby enhancing the disinfecting effect with respect to the contact lens. Like the conventional contact lens liquid agent, the present disinfecting liquid permits a visual observation of the contact lens immersed therein.
In another preferred form of the above first aspect of the present invention, the disinfecting liquid further contains sodium chloride. The inclusion of sodium chloride assures an enhanced disinfecting effect of the disinfecting liquid with respect to the contact lens. In the present disinfecting method, it is preferable to apply ultrasonic waves to the disinfecting liquid or oscillate the disinfecting liquid, prior to or upon incidence of the light thereon, so that the fine particles of the titanium oxide can be uniformly dispersed in the disinfecting liquid to assure a further improved disinfecting effect.
When the disinfecting liquid includes the sodium chloride, the concentration of the sodium chloride is preferably held in a range of 0.7xcx9c1.2 wt. %. Even if the disinfecting liquid may enter the eye of the lens user when the contact lens which has been disinfected according to the present disinfecting method is worn on the eye with the disinfecting liquid adhering to the surfaces of the contact lens, the disinfecting liquid containing the sodium chloride whose concentration is kept within the above range is effective to reduce eye irritation.
In a further preferred form of the above first aspect of the present invention, the disinfecting liquid further contains, as needed, at least one of a chelating agent, a buffer, a surface active agent, a thickener, a preservative, a germicide, and an oxidizing agent, so that the disinfecting liquid has an intended property given by the at least one additive.
The oxidizing agent is preferably selected from among a hydrogen peroxide, ozone water, a sodium peroxide, a magnesium peroxide, and a silver oxide, for instance. It is particularly preferable to use the hydrogen peroxide to promote the photocatalytic action of the fine particles of the titanium oxide. For preventing the peroxide remaining in the disinfecting liquid from adversely influencing the eye of the lens user, the hydrogen peroxide is contained in the disinfecting liquid preferably in a concentration of 10xcx9c300 ppm.
Preferably, the disinfecting liquid further contains at least one metal ion, together with the hydrogen peroxide.
In a still further preferred form of the above first aspect of the present invention, the light is selected from the group consisting of a natural light, an ultraviolet light, a visible light, a light emitted from an incandescent lamp, and a light emitted from a fluorescent lamp.
In a yet further preferred form of the above first aspect of the present invention, the disinfecting liquid is irradiated with the light having a wavelength of 320xcx9c410 nm.
In another preferred form of the above first aspect of the invention, the light has an intensity in a range of 0.1xcx9c50 mW/cm2 at a wavelength of about 365 nm.
The above-indicated second object of the present invention may be attained according to a second aspect of the invention, which provides a contact lens disinfecting liquid which exhibits a disinfecting effect with respect to a contact lens by being irradiated with a light, the contact lens disinfecting liquid being characterized by containing water-dispersible fine particles of a titanium oxide which are dispersed in an aqueous medium.
A contact lens is immersed in the present contact lens disinfecting liquid wherein the titanium oxide is dispersed in a suitable aqueous medium in the form of fine particles, and the disinfecting liquid is irradiated with a light, so that the fine particles of the titanium oxide exhibit an excellent disinfecting or germicidal action based on the photocatalytic action thereof. Further, the disinfecting action of the titanium oxide lasts for a long period of time. Moreover, the present disinfecting liquid is safe and simple to handle.
In a preferred form of the above second aspect of the present invention, the fine particles of the titanium oxide have an average particle size of not larger than 15 nm. Preferably, the fine particles of the titanium oxide are contained in the disinfecting liquid in a concentration of 1xcx9c100 ppm. As in the above-described first aspect of the present invention, it is preferable that the contact lens disinfecting liquid according to the second aspect of the invention further contains sodium chloride.
As needed, the present contact lens disinfecting liquid may further contain an oxidizing agent such as a hydrogen peroxide.
In a preferred form of the above second aspect of the present invention, the contact lens disinfecting liquid further contains at least one metal ion, together with the oxidizing agent.